This invention relates to the field of ceramics and particularly to dense polycrystalline tungsten carbide inserts with chip control.
In the machining process, it is important for the cutting tool to work effectively at high speeds and to have a long tool life. In order for the cutting tool to be effective, it must be made of a material which results in the tool having a high heat hardness and a high transverse rupture strength and fracture toughness, and it must also have a design sufficient to control the flow of chips which are formed in the machining process and to reduce the cutting forces.
Chip control is an important element ofthe machining process, in order to break up the length of undesirably long chips which may be formed in the machining process. In high speed machining, if the strip taken off from the workpiece by the cutting insert is not broken up, the strip can interfere with the machining process in a variety of ways. For example, an undesirably long chip can be re-cut and welded onto a portion of the workpiece, thereby causing poor surface conditions on the workpiece. An undesirably long chip, if not broken under chip control, can also cause breakage of the machining tool itself. Additionally, undesirably long chips can feed into the tool holder or other portions of the machine and cause difficulties, e.g., damaging parts of the tool holder or obstructing visibility of the working area. Further, long ribbons are difficult to handle and can represent a safety hazard to the machine operator. Accordingly, there is a need in the high speed machining process to provide chip control. One method for controlling chip production is to incorporate an insert into the cutting tool, with the insert providing the means for chip control. Many different types of ceramic cutting tools with chip control inserts have been described, including those in U.S. Pat. Nos. 5,628,590; 5,141,367; and 5,330,296, the contents of which are hereby incorporated in their entirety.
In addition to chip control, another important aspect of cutting tools are the materials of which they are made. Cutting tools have been made with ceramics and ceramic-metal composites (xe2x80x9ccermetsxe2x80x9d), including tungsten carbide (xe2x80x9cWCxe2x80x9d). Early work with WC focused upon densifying WC by heating to a temperature of, for example, 2,000xc2x0 C. The densified material was judged unsuitable for use in applications requiring toughness, such as in cutting tools. The unsuitability stemmed largely from the densified material""s excessively brittle character.
Efforts to overcome or offset some of the brittleness led to incorporation of an amount of a metal by admixing powdered metal and WC powder to form a composite and densifying the composite at a temperature above that at which the metal melts. The metal, most frequently an iron group metal (iron, cobalt or nickel), was added to impart some of its ductility to the composite. The densified composites, also known as cemented carbides, cermets and hard metals, have been used extensively for several decades in machining tools. In order to increase the cutting speed and cutting efficiency, a variety of additions have been made to the composition of ceramic cutting tools.
In general, hardness of the cermets,(i.e., wear resistance and strength and toughness, i.e., fracture resistance of a hard alloy) can be changed by tungsten carbide particle size, cobalt content and additional amounts of other carbides. The resulting hardened alloy has been widely used for various purposes. However, in formulating these materials, there is a tendency that if wear resistance is heightened, fracture resistance is lowered, and conversely, if fracture resistance is heightened, wear resistance is lowered. Therefore, in the design of cermet cutting tools, there has been encountered the problem of improving one material property at the expense of another material property by adding cobalt or another iron group that will plastically deform in the heat of high speed machining.
There have been many attempts to solve this problem, including removing the machining equipment from use and reprofiling the cemented carbide cutting tool in order to reestablish its desired properties and scrapping the used cemented carbide portion and inserting a new cemented carbide portion with the desired properties. There currently exists a need for machining tools with chip control which can maintain the desired machining properties of wear resistance and breakage resistance during high heat high speed machining.
Although cermets and WC have been used extensively in the design of cutting tools, there still has not been a satisfactory resolution to the problem of tailoring the composition of the cermet or WC in order to maximize efficiency of the cutting tool. The present invention solves this problem by incorporating into a machining tool a chip control insert made of WC. Such inserts have not been previously used, and such inserts maximize the efficiency of machining tools.
Cutting tool inserts with chip control composed of essentially dense, fine grained polycrystalline, tungsten carbide (WC) are included in the present invention.
According to the present invention, the ceramic cutting insert for high speed machining includes a cutting edge, a rake face with a chip control groove surface, a flank face and the cutting edge that is formed at the juncture of the flank face and the rake face.
These components are made by ceramic processing techniques and result in a ceramic body which has a density of greater than 95% of its theoretical density with substantially all grains having an average size of 0.001 to 20 micrometers.
In other aspects the insert is comprised of polycrystalline tungsten carbide of at least 98.5% by volume tungsten carbide. In another aspect an iron group, e.g. cobalt is present in the ceramic body from 0.01% to 1.5% by volume.
A further aspect of the present invention is to control the grain size of the tungsten carbide by adding an inert second phase such as refractory oxides, carbides, nitrides or borides.
The ceramic articles of this invention are particularly useful as wear parts, especially as cutting tools for a wide variety of materials, including the machining titanium metals and alloys of titanium which have a very high content of titanium, cast iron, aluminum, high nickel alloys, stainless steels, wood machining-cutting, and high speed machining of steels.